1. Field of the Invention
The present invention concerns a heating tip used as a soldering tip, a hot knife or a hot blow tip in which a heat generating portion such as an electric heater or a gas combustion catalyst part is inserted and contained in an insertion cavity and a method of manufacturing such a heating tip and, more in particular, it relates to a heating tip capable of improving the heat conduction efficiency and the temperature rising characteristic of a tip, as well as a method of manufacturing such a heating tip.
2. Statement of Related Art
In a case of manufacturing a heating tip such as a tip of an electric soldering iron, a tip substrate is formed by applying iron plating on a surface of a cylindrical copper substrate. Then, the tip substrate is shaped by forging and then an insertion cavity is formed by cutting in the base end of the tip substrate for containment of a heat generating portion by using a cutting tool, for example, a drill or a bit as disclosed in U.S. Pat. No. 4,500,027 (Japanese Patent Publication Sho 59-11386).
In the method of manufacturing the heating tip as described above, the insertion cavity for the heat generating portion is usually formed by drilling or like other cutting. In the cutting operation, however, since a great amount of cutting chips are discharged wastefully, they result in a problem of increasing the material cost and also increasing a burden for disposal of wastes. This is particularly remarkable when the depth of the insertion cavity is large relative to the entire length of the heating tip.
Further, when the insertion cavity is formed by using a drill, since long twisted chips are formed continuously, they require considerable period of time to treat them. This drawback may be avoided by fabricating the insertion cavity while reciprocating the drill but this increases the operation time and lowers the productivity.
Further, when the insertion cavity is formed by cutting after the iron plating, plated iron is mixed in the chips of copper, to make the recycling operation of the copper chips difficult. If copper and iron can not be separated completely, it results in a problem that the commercial value of the copper chips in reuse is remarkably reduced. This problem may be solved by mechanically cutting off to remove the rear end portion of the heating tip before forming the insertion cavity. However, since the cut off pieces falls on the same place as that for the copper chips, they can not be separated easily.
Further, before cutting fabrication, centering has to be conducted accurately from the outside of the iron plating layer. However, since the thickness of the plating layer is not always uniform, centering for the insertion cavity may often be displaced to bring about a problem that the heating tip can not be heated uniformly by the heat generating portion.
Further, since it is almost impossible to mirror finish the inner circumferential surface of the insertion cavity by cutting fabrication, oxide scales are formed during use to worsen the heat efficiency.
In view of the above, electroless plating is sometimes adopted to the inner wall surface of the insertion cavity. However, if chips formed in the preceding cutting step remain in the insertion cavity, they are dissolved in the plating solution and break the balance of the composition of the plating solution, failing to obtain a satisfactory plating layer.
Even if a satisfactory plating layer can be obtained, there is still present a problem that the plated layer is defoliated in an extremely short period of time since the surface of the insertion cavity is not smooth.
Then, a stainless steel pipe is sometimes inserted instead of applying plating in the insertion cavity. However, since the heat conductivity is extremely poor in the case of using stainless steel, this leads to a problem that the heat efficiency of the tip is worsened extremely.
Further, even if a super-hard drill or the like is used, in a case of the cutting operation, the drill is abraded rapidly and results in a problem that the bore diameter of the insertion cavities varies greatly.
Finally but most importantly, the cross sectional shape of the insertion cavity can not be formed in any other shape than the circular shape by drill-cutting, so that the heat generating portion also has to be formed to a circular cross sectional shape. However, for a certain identical volume, a circular circumferential shape gives the smallest surface area among other shapes, and this results in a problem of deteriorating the heat conductivity between the outer circumference of the heat generating portion and the inner wall circumference of the tip cavity.